A conventional bicycle has a hub, a gear and a clutch positioned at a rear end of the bicycle. The clutch connects the hub and the gear. The rotational drive force generated by a bicycle rider transmits from the pedals to the gear through the chain so that the gear is able to drive the hub to rotate through the clutch. However, when the rotational drive force generated by the bicycle rider disappears, such as the rider stops pedaling the pedals or pedals the pedals in an opposite direction, the clutch disconnects the hub and the gear so that the hub keeps rotating relative to the gear, freely.
A ratchet assembly is used as a clutch in conventional bicycles. The ratchet assembly includes a pawl seat on which a plurality of steel pawls are installed and a gear with a plurality of teeth. The steel pawls slantingly protrude out from the surface of the pawl seat at an interval between each of the steel pawls. The teeth protrude out from the gear surface at an interval between each tooth. Each tooth of the gear has one edge with a moderate slope and another edge with a steep slope. The steel pawls engage with the teeth, respectively. When the pawl seat is rotating relative to the gear in the restricted direction, i.e., rotating forward, the steel pawls catch against the edges of the teeth with the steep slope, respectively, so that the pawl seat cannot rotate relative to the gear in the restricted direction. When the pawl seat is rotating relative to the gear in the unrestricted direction, i.e., rotating backward, the steel pawls easily slide across the edges of the teeth of the gear with the moderate slope, respectively, so that the pawl seat can freely rotate relative to the gear in the unrestricted direction.
However, there are intervals between the steel pawls on the pawl seat and the teeth of the gear in the conventional ratchet assembly. When the pawl seat is rotating relative to the gear in the restricted direction, the pawl seat needs to rotate about an angle relative to the gear before the steel pawls can mesh with the edges of the teeth with the steep slope, respectively. Therefore, the steel pawls may not catch on the teeth in time, causing the rotational energy to be transmitted discontinuously.
Moreover, when the pawl seat is rotating relative to the gear in the unrestricted direction, interference is generated at the contact surface between the steel pawls and the teeth, respectively, because the steel pawls need to slide across the edges of the teeth. Therefore, the interference may waste energy when the conventional ratchet assembly is used as a clutch.